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Coolant temp issues after turning off and restarting engine 1.8 AWM

1K views 10 replies 4 participants last post by  Tomvw 
#1 · (Edited)
Ever since my friend removed my radiator and did a full timing belt, water pump, thermostat service I have had an issue with the coolant temp on my car and I think it is related somehow to the auxilary fan. The coolant temp gauge never goes above middle while driving or at idle, but if I turn off the engine to go into a store or get fuel and then restart the engine the temp gauge goes up on or two ticks above middle but then goes back to normal shortly after I start to drive.
The scan tool shows my temp around 194-196 but does fluctuate to 200 and then back down.

I checked the fan on the passenger side and it doesn't appear to be turning on while the car is running, although when I turn the ac on the fan moves just fine. I thought that there was an autorun feature on the fan after the car was turned off, but I can't find confirmation on this and don't know if changing the sensor (thermal switch) in the lower radiator hose is what I need to do or if I need to change any of the fan relays or a fuse. I don't think changing the coolant temp sensor on the back of the engine makes any sense.

If anybody knows anything about the autorun feature or how best to troubleshoot the fan issue I would appreciate advice or direction.

Thanks

This is for my 01 A4 1.8
 
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#3 ·
I have ordered the coolant temp sensor because it is a cheap and easy fix, and I also purchased the aux fan thermo switch (4pin) that plugs into the radiator hose. I recall that the electric fan used to run after turning the engine off to help it cool down but now it doesn't do that. Maybe it never did and I am just imagining that. Not quite sure.
 
#5 ·
Thanks Tom for the reply. I am not necessarily worried that any damage will be done, but I am curious why the gauge suddenly started acted erratically. I also seem to be having slightly higher than normal oil temps so I think that something is faulty but I don't know if I will ever figure out whether I have a faulty thermostat, fan switch/module, or coolant temp sensor. I will still replace the the temp sensor and switch and see if the problem still persists and report back in a few days. Cheers
 
#8 ·
Update- Pulled the green coolant temp sensor and there were bits of pink colored thin plastic looking shavings around the temp sensor and the o-ring was totally destroyed. It hadn't been leaking coolant but it was ready to go. Will report back if this stops the gauge from acting erratic.
 
#10 ·
That makes sense since the o-ring had basically turned to mush. I pulled the thermal switch and drained the coolant system last night and that o-ring was fine and I am guessing the switch was still functional but replaced it anyway. The coolant had a good amount of silt in it but nothing that I would be worrying about. Refilled and burped the coolant system and the aux fan still only runs with a/c. I will update if any issues come up
 
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